Wireless headset systems are used for hands free talking via a mobile terminal or a base station. In automobiles, for example, headsets allow the use of mobile terminals without the necessity to hold the mobile terminal to the head while being in a conversation and thus, the driver of a vehicle may use both hands to control the automobile.
Most conventional wireless headsets are held on the head by a head band or a preshaped rigid supporting portion (ear hook), which is to be mounted behind the ear. A speaker portion is placed in the ear orifice, and a rigid microphone supporting boom extents towards the mouth. Microphone and speaker are connected to a transceiver for transmitting/receiving a voice signal via an antenna. The communication can be based on a communication protocol, such as the Bluetooth™, the WLAN (Wireless Local Area Network), the UMTS (Universal Mobile Telecommunication Systems), or the GSM (Global Systems for Mobile communication) protocol.
Nowadays, headsets have to be as small as possible, and nevertheless functional. In particular, high power efficiency, good acoustical and antenna performance are desired. Thereby, the antenna design is a main factor for the size of the headset, especially in the case when the antenna has to achieve a sufficient bandwidth to fulfill the requirements of the above communication protocols. Such antennas require a certain ground plane size to achieve the desired bandwidth. Generally, small antennas have a lower efficiency than big antennas, wherein a low efficiency wastes battery power.
A headset having a built-in wideband antenna which requires a small ground plane is described in EP1416585A1. In this design, the antenna arrangement has a three-dimensional structure, like a rectangular box, wherein one of the planes is the printed circuit board (PCB), on which the grounding layer and the radio circuits are provided. Although said document suggests to place components such as batteries inside the antenna structure, there is a lot of space that cannot be used for any other purpose. However, the ideal solution has no unused space (air) inside the product.